Seismic isolator

ABSTRACT

A seismic isolator comprising: a first and a second plate-like coupling member which are arranged substantially horizontally one spaced apart above the other; and a movable sliding-block which is interposed between said plate-like coupling members, and rests in a freely sliding manner on the concave bottom of a depression realized on the exposed face of said first plate-like coupling member; the concave bottom being provided with at least one free-sliding area, which surrounds/flanks the stationary-standing area and is provided with a dynamic friction coefficient greater than that of the stationary-standing area.

TECHNICAL FIELD

The present invention concerns a seismic isolator.

In greater detail, the present invention concerns a seismic isolator forsmall buildings, use to which the following discussion will makeexplicit reference without losing in generality.

BACKGROUND ART

As is known, seismic isolators are devices which are usually interposedbetween the foundation basement and the superstructure of the building,and are structured so as to reduce and at least partially dissipate themechanical stresses which are transmitted to the superstructure of thebuilding during seismic events.

The seismic isolators currently on the market are basically divided intotwo categories: elastomeric-type seismic isolators and pendular or“sliding” seismic isolators.

The elastomeric-type seismic isolators are basically made up of twocoupling plates made of metal material, which are arranged horizontallyand spaced one above the other; and of a large block of elastomericmaterial, which is interposed between and securely attached/anchored toboth the coupling plates, and incorporates inside itself a series ofmetal sheets arranged horizontally and spaced above one another.

The lower coupling plate is structured so as to rest on and be stablyanchored to the foundation basement of the building, while the uppercoupling plate is structured so as to stably anchored underneath thesuperstructure of the building.

The block of elastomeric material is able to deform in presence ofhorizontal shear stresses, thus allowing the upper coupling plate tomove horizontally with respect to the lower coupling plate, consequentlymodifying the dynamic behaviour of the isolated structure.

Sliding seismic isolators, on the other hand, are basically made up oftwo coupling plates made of metal material, which are arranged inhorizontal position spaced one above the other; and of a largeintermediate movable sliding-block which has a substantiallynon-deformable structure and rests in free sliding manner on both thecoupling plates.

In greater detail, the intermediate sliding-block rests in free slidingmanner on the concave bottom of a large lenticular-shaped depressionwhich is formed in the centre of the exposed face of the upper and/orlower coupling plate.

Also in this case the lower coupling plate is structured so as to bestably anchored resting on the foundation basement of the building,while the upper coupling plate is structured so as to be stably anchoredunderneath the base of the superstructure of the building.

During the seismic event, the sliding seismic isolator allows thesuperstructure of the building to move freely in a horizontal directionwith pendular movement, dissipating by friction a part of the seismicenergy. At the end of the seismic event, instead, the concave profile ofthe bottom of the depression allows self-centring of the superstructureof the building on the foundation.

Unfortunately, although offering a high capacity of absorbing seismicwaves, the elastomeric-type seismic isolators have an unstable behaviourin the presence of relatively reduced vertical loads, like those typicalof a small building, therefore they are not suitable for isolating thesetypes of buildings.

The sliding seismic isolators, on the other hand, are generally toocostly to be used in small buildings, and furthermore they do not offerthe same performance as the elastomeric-type seismic isolators.

DISCLOSURE OF INVENTION

Aim of the present invention is to provide a sliding seismic isolatorwith better performance than those currently known, and which is alsocheaper to produce.

In compliance with the above aims, according to the present inventionthere is provided a seismic isolator as defined in claim 1 andpreferably, though not necessarily, in any one of the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to theaccompanying drawings, which illustrate a non-limiting embodimentexample thereof, in which:

FIG. 1 is a partially exploded perspective view of a seismic isolatorrealized according to the teachings of the present invention;

FIG. 2 is a section view of the seismic isolator shown in FIG. 1, withparts removed for clarity; whereas

FIG. 3 is a section view of a second embodiment of the seismic isolatorshown in FIG. 1, with parts removed for clarity.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to FIGS. 1 and 2, number 1 denotes as a whole a seismicisolator adapted to be interposed between the superstructure of abuilding and the foundation basement or other substructure of the samebuilding, so as to significantly reduce the stresses transmitted to thesuperstructure of the building during seismic events.

Obviously, the seismic isolator 1 can also be interposed between thebase of a marble statue and the supporting plane underneath, between thedeck and the piers of a bridge, or between the ground resting feet of alarge object (for example a large high voltage transformer) and theunderlying reinforced concrete base, again in order to significantlyreduce the mechanical stresses transmitted to the statue or to the largeobject during seismic events.

With reference to FIGS. 1 and 2, the seismic isolator 1 comprises: afirst substantially non-deformable, plate-like coupling member 2 whichextends horizontally and is adapted to be arranged with its lower face 2b stably resting on the ground or other supporting plane; asubstantially non-deformable, movable sliding-block 3 which rests infree sliding manner on the exposed upper face 2 a of the plate-likemember 2; and a substantially non-deformable, second plate-like couplingmember 4 which extends horizontally spaced above the plate-like member2, is adapted to be arranged with its upper face 4 b stably restingunderneath the body to be seismically isolated, and lastly rests in freesliding manner on the top of the sliding-block 3.

In other words, plate-like members 2 and 4 are arranged in asubstantially horizontal position spaced one above the other, and themovable sliding-block 3 rests in free sliding manner on surface of theexposed upper face 2 a of plate-like member 2 and on surface of theexposed lower face 4 a of plate-like member 4.

In greater detail, the lower plate-like member 2 is preferably made ofmetal material, and is preferably structured to be rigidly anchored onand in abutment with the foundation basement P or other substructure ofthe building to be seismically isolated.

Similarly, the upper plate-like member 4 is preferably made of metalmaterial, and is preferably structured to be rigidly anchored inabutment beneath the superstructure (not shown) of the building to beseismically isolated.

Likewise to plate-like members 2 and 4, also the movable sliding-block 3is preferably made of metal material.

In greater detail, in the example shown, the plate-like member 2 and/orthe sliding-block 3 and/or the plate-like member 4 is/are preferablymade of steel. Preferably the resting surfaces of the sliding-block 3are furthermore covered with a layer of Teflon (polytetrafluoroethylene)or other similar material.

In a different embodiment, however, the sliding-block 3 could be made ofhigh-strength plastic or composite material. For example, thesliding-block 3 could be made of reinforced rubber and optionally havethe resting surfaces coated in Teflon or other similar material.

With reference to FIGS. 1 and 2, in particular, the exposed upper face 2a of plate-like member 2 is provided, preferably in a substantiallycentral position, with a broad depression 5 which has a concave bottom 6with radius of curvature R preferably substantially constant; and thesliding-block 3 rests in free sliding manner on the concave bottom 6 ofthe depression 5, within the perimeter of a given stationary-standingarea/zone 6 a which has an extent smaller than the overall extent of theconcave bottom 6 and is preferably located at the point in which thedepth of the depression 5 is maximum.

In other words, the movable sliding-block 3 is preferably arrangedresting on the concave bottom 6 of the depression 5 in a position ofstable equilibrium.

Preferably the lower part 3 a of movable sliding-block 3 further has ashape locally substantially complementary to that of the concave bottom6 of depression 5.

With reference to FIGS. 1 and 2, in the example shown, in particular,the depression 5 present on the exposed upper face 2 a of plate-likemember 2 is substantially lenticular in shape.

In greater detail, the concave bottom 6 of depression 5 is preferablyshaped substantially like a spherical dome, and the lower part 3 a ofmovable sliding-block 3 has a shape complementary to that of the restingpoint on the concave bottom 6.

In other words, the movable sliding-block 3 rests on the concave bottom6 of depression 5 with a resting surface 3 a shaped substantially like aspherical dome having a radius of curvature substantially equal to theradius of curvature R of the concave bottom 6.

Preferably the stationary-standing area 6 a furthermore is substantiallycircular in shape and is preferably located substantially in the centreof the concave bottom 6 of depression 5.

With reference to FIGS. 1 and 2, in addition the concave bottom 6 ofdepression 5 also has one or more free-sliding areas that surround/flankthe stationary-standing area 6 a and have a dynamic friction coefficientgreater than that specific of the stationary-standing area 6 a; and themovable sliding-block 3 is able to slide freely on the concave bottom 6of depression 5 also above said free-sliding areas.

Preferably the value of the dynamic friction coefficient increases asthe distance of the free-sliding area from the perimeter of thestationary-standing area 6 a raises.

With reference to FIGS. 1 and 2, in the example shown, in particular,the concave bottom 6 of depression 5 preferably has two annular-shapedfree-sliding areas 6 b and 6 c, which are concentric to each other andcompletely surround the stationary-standing area 6 a.

Free-sliding area 6 b completely surrounds the stationary-standing area6 a, and has a dynamic friction coefficient preferably ranging from 110%to 130% of the dynamic friction coefficient specific of thestationary-standing area 6 a.

Free-sliding area 6 c completely surrounds the free-sliding area 6 b,and has a dynamic friction coefficient preferably ranging from 130% to150% of the dynamic friction coefficient specific of thestationary-standing area 6 a.

Preferably the free-sliding areas 6 b and 6 c are also adjoined/adjacentto each other.

In greater detail, assuming that plate-like member 2 and movablesliding-block 3 are preferably made of steel and that the steel-steeldynamic friction coefficient at the stationary-standing area 6 a isequal to approximately 0.42, the free-sliding area 6 b has a dynamicfriction coefficient preferably ranging from 0.44 to 0.54. Thefree-sliding area 6 c, on the other hand, has a dynamic frictioncoefficient preferably ranging from 0.54 to 0.63.

With reference to FIGS. 1 and 2, in the example shown, in particular,the plate-like member 2, the movable sliding-block 3 and the plate-likemember 4 preferably consist of an equal number of monolithic blocks madeof high-strength steel.

Preferably the plate-like member 2 is moreover structured so as to bestably anchored to the ground, or better to the foundation basement P ofthe building, by means of a series of anchoring bolts 7 or othermechanical anchoring elements of known type.

With reference to FIG. 2, the surface of concave bottom 6 correspondingto the free-sliding area 6 b is preferably coated with a layer of castiron 8. The surface of concave bottom 6 corresponding to thefree-sliding area 6 c, on the other hand, is preferably coated with alayer of semi-metallic carbon ceramic material 9.

Alternatively, at the free-sliding areas 6 b and/or 6 c, the surface ofconcave bottom 6 may be sandblasted or surface-machined so as to locallyincrease the roughness of the surface, thus increasing the steel-steeldynamic friction coefficient.

With reference to FIGS. 1 and 2, similarly to the exposed face 2 a ofplate-like member 2, the exposed lower face 4 a of plate-like member 4is preferably provided, in a substantially central position, with abroad depression 12 having a substantially horizontal flat bottom 13;and the upper end 3 b of movable sliding-block 3 rests in free slidingmanner on the flat bottom 13 of depression 12.

Preferably the upper end 3 b of movable sliding-block 3 moreover restson the flat bottom 13 of depression 12 inside the perimeter of a givenstationary-standing area/zone 13 a that has an extent smaller than theoverall extent of flat bottom 13, and is preferably located in thecentre of the exposed face 4 a of plate-like member 4; and the movablesliding-block 3 is able to slide freely on the flat bottom 13 ofdepression 12 also outside the stationary-standing area/zone 13 a.

With reference to FIGS. 1 and 2, likewise plate-like member 2, in theexample shown the plate-like member 4 preferably consists of amonolithic block made of high-strength steel, and is preferablystructured to be stably anchored beneath the large body to beseismically isolated by means of a series of anchoring bolts 14 or othermechanical anchoring elements of known type.

Operation of seismic isolator 1 is easily inferable from the abovedescription and does not require further explanations.

The advantages connected to the particular structure of seismic isolator1 are remarkable.

Computer simulations have highlighted that, due to the free-slidingareas 6 b, 6 c with increased dynamic friction coefficient, the seismicisolator 1 is able to dissipate much more seismic energy than atraditional pendular seismic isolator, with all the ensuing advantages.

In addition, seismic isolator 1 has particularly restrained productioncosts and is therefore suitable for installation on small buildings.

Clearly modifications and variations can be lastly made to seismicinsulator 1 without however departing from the scope of the presentinvention.

For example, the depression 5 having the concave bottom 6 could berealized on the exposed face 4 a of upper plate-like member 4.

Or the depression 12 present on the exposed face 4 a of upper plate-likemember 4 could have a concave bottom with substantially constant radiusof curvature.

With reference to FIG. 3, furthermore, in a more sophisticatedembodiment the upper plate-like member 4 could comprise: two metallicplates 15 and 16 arranged in a substantially horizontal position, spacedone above the other; and an intermediate layer of elastomeric material17 of suitable thickness which is interposed between and securelyattached/anchored to the surface of metallic plates 15 and 16.

The upper metallic plate 15 is structured to be stably anchored beneaththe superstructure of the building (not shown) or another large objectto be seismically isolated.

The lower metallic plate 16 rests in free sliding manner on the upperpart 3 b of movable sliding-block 3.

In a less sophisticated embodiment, moreover, the movable sliding-block3 may be rigidly integral with the exposed face 4 a of upper plate-likemember 4.

Lastly, the plate-like member 2 and/or the plate-like member 4 mayconsist of a preformed metal sheet with reduced thickness, cast on ablock of epoxy resin or cement.

In other words, also the plate-like member 2 and/or the plate-likemember 4 could be made of composite material.

1. A seismic isolator comprising: a first and a second plate-likecoupling member which are arranged substantially horizontally one spacedapart above the other; and a movable sliding-block which is interposedbetween said plate-like coupling members, and rests in free slidingmanner on the concave bottom of a depression realized on the exposedface of said first plate-like coupling member; the seismic isolatorbeing characterized in that the movable sliding-block rests in a freesliding manner on said concave bottom, within the perimeter of a givenstationary-standing area (6 a) having an extent smaller than the overallextent of the concave bottom; and in that the concave bottomadditionally has at least one free-sliding area which surrounds/flankssaid stationary-standing area and is provided with a dynamic frictioncoefficient greater than that of the stationary-standing area; themovable sliding-block being able to freely slide on the concave bottomof the depression also above said free-sliding area.
 2. Seismic isolatoraccording to claim 1, characterized in that the concave bottom has aradius of curvature substantially constant.
 3. Seismic isolatoraccording to claim 2, characterized in that said concave bottom isshaped substantially like a spherical dome, and in that thestationary-standing area is located substantially at the centre of saidconcave bottom.
 4. Seismic isolator according to claim 3, characterizedin that said at least one free-sliding area is annular in shape andcompletely surrounds the stationary-standing area.
 5. Seismic isolatoraccording to claim 1, characterized in that the concave bottom has aplurality of free-sliding areas which surround/flank saidstationary-standing area and are provided with a dynamic frictioncoefficient greater than that of the stationary-standing area; themovable sliding-block being able to freely slide on the concave bottomof the depression also above said free-sliding areas.
 6. Seismicisolator according to claim 5, characterized in that the free-slidingareas are adjacent/adjoined to each other.
 7. Seismic isolator accordingto claim 5, characterized in that the value of the dynamic frictioncoefficient increases as the distance of the free-sliding area from thestationary-standing area raises.
 8. Seismic isolator according to claim1, characterized in that the movable sliding-block rests in free slidingmanner also on the exposed face of said second plate-like couplingmember.
 9. Seismic isolator according to claim 1, characterized in thatthe movable sliding-block is rigidly integral with said secondplate-like coupling member.
 10. Seismic isolator according to claim 1,characterized in that said first plate-like coupling member is made ofmetal material and/or in that said second plate-like coupling member ismade of metal material.
 11. Seismic isolator according to claim 1,characterized in that said movable sliding-block is made of metalmaterial or plastic material or composite material.
 12. Seismic isolatoraccording to claim 1, characterized in that said first plate-likecoupling member is adapted to be stably anchored to the ground or toanother supporting surface, and in that said second plate-like couplingmember is adapted to be stably anchored beneath the superstructure ofthe building or other body to be seismically isolated.